Reports on Plant Diseases |
RPD No. 700 - Raspberry Anthracnose
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April 2001
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[ Symptoms ] [ Disease
Cycle ] [ Control ]
| Raspberry anthracnose, caused by the fungus Elsinoe
veneta, is the most common and widespread disease of brambles.
The disease is most destructive on black and purple raspberries. Although
red raspberries, blackberries, dewberries, and loganberries are commonly
affected, anthracnose is not usually as serious on these brambles.
The disease infects the canes, leaves, fruit, and stems of berry clusters.
Losses result from defoliation, a general stunting and decrease in
cane vigor, a reduction in fruit yield and quality, and the death
of the canes. Infected canes are more susceptible to winter injury
and other diseases than healthy canes. If left uncontrolled for a
year or more, the raspberry anthracnose can cause an almost total
crop loss.
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Figure
1.
Anthracnose lesions on black raspberry primocane (courtesy B.
Williamson).
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Symptoms
Canes. Small, roundish, slightly raised, purple lesions
appear on young canes. These lesions enlarge up to about 3/8 inch
(9 mm) in diameter and become oval shaped. The centers become somewhat
sunken and pale buff to ash gray in color, with the margins somewhat
raised and purple (Figure 1). If numerous, the lesions merge and
cover large portions of the cane (Figure 2) giving a "graybark"
appearance. As cane infections progress, lesions become sunken,
cracked, and very rough. Infected canes dry out, weaken, and often
die during the winter or break off during their fruiting year.
Fruit, Leaf, and Flower Stems. These plant parts
develop small, elongated, gray lesions similar to those described
on the canes. Fruiting stems girdled will curl and crack. Fruit
produced on these stems is small, hard, dry, and seedy. In rainy
weather, individual berry drupelets become rusty brown, scabby,
and shrunken.
Leaves. The anthracnose disease also appears on the
upper leaf surface in early to midsummer and appears as irregular,
yellowish white spots about 1/16 inch (1.5 mm) in diameter (Figure
3). The spots gradually enlarge, develop a reddish purple margin
around a light gray center. The infected leaf tissue may drop out,
producing a "shot-hole" effect (Figure 3). Severe leaf
infection may cause premature defoliation.
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Figure
2.
Late season anthracnose on raspberry canes..
Figure
3.
Anthracnose infecting a raspberry leaf.
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Disease Cycle
The fungus overwinters as mycelium, ascocarps, or acervuli within lesions
on overwintering canes. In the early spring, the fungus produces two types
of microscopic spores (conidia and ascospores) that are rain-splashed,
blown, or carried by insects to young, actively growing cane and leaf
tissues. The spores germinate in a film of moisture in 3 to 12 hours and
infect young tissues; new spots appear about a week later. As the canes
mature, they become hardened and more resistant to infection. Spores (conidia)
are released and spread during late August and September rains. Numerous
dark specks (pimplelike acervuli), often arranged in radiating patterns,
develop within lesions. These lesions produce the conidia for infections
the following spring, thus completing the disease cycle.
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Control
Raspberry anthracnose is not difficult to control if the outlined recommendations
are followed.
- Choose a sunny planting site with good soil and air drainage. Avoid
shady areas. The more rapidly the canes and foliage dry following dew,
rain, or overhead irrigation, the less chance there is for anthracnose
to develop.
- Start with planting stock that is certified, No. 1 grade, one year
old, and virus-free. Always purchase plants from reputable nurseries.
Never take plants from a friend or from an established bramble
patch. When setting out new plants in the early spring, cut off the
"handles" (old cane stubs) at ground level. New shoots will
appear from the crown. At the same time, remove all dead and winter-injured
canes from the planting site. Destroy these prunings before new
shoots appear. Infections on these canes are the source of anthracnose
infections on new plants. In addition, remove all wild or neglected
raspberries and blackberries in the area.
- To maintain plant vigor, fertilize raspberries as needed, but avoid
using excessive amounts of fertilizer.
- Keep the fruit-planting area free of weeds. Cultivate carefully to
reduce root injury. Keep rows about 12 to 18 inches (30 to 45 cm) wide
for better air circulation, penetration of sunlight, and good spray
coverage.
- Remove and destroy all infected and old fruited canes immediately
after harvest. Prune close to the ground. Thin the new canes to about
6 for staked-hill plantings, or 4 to 6 inches (10 to 15 cm) apart for
hedge rows. Thin out all weak, short, spindly, and injured canes.
- Follow the raspberry spray schedule outlined in the "Illinois
Commercial Small Fruit and Grape Spray Guide" (website: http://www.hort.purdue.edu/hort/ext/sfg/).
Thorough coverage of all canes and foliage with each application is
essential. If possible, apply the spray prior to rain. The spray material
must be dry before the rain starts.
- In the spring, spray when the buds show no more than 3/8 inches (1
cm) of green at the tips. Where anthracnose has been severe, spray again
when the new canes are 6 to 8 inches(15 to 20 cm) tall; or just before
the blossoms open on the fruiting canes; just after bloom as soon as
the petals fall; and just after the fruit has been harvested and old
canes removed. Consult the raspberry spray schedule for recommendations
as to spray materials and rates recommended for controlling bramble
diseases.
- Keep raspberry plantings free of insects such as crown borers, stem
girdlers, aphids, fruitworms, rose scale, sawflies, plant bugs, tree
crickets, picnic and sap beetles, and mites. Follow the cultural and
chemical control suggestions given in the "Midwest Small Fruit
Pest Management Handbook" (Website: http://www.ag.ohio-state.edu/~ohioline/b861/index.html)
and "Illinois Commercial Fruit and Grape Spray Guide." Also,
more information is available in the "Compendium of Raspberry and
Blackberry Diseases and Insects", published by the American Phytopathological
Society, St. Paul, Minnesota.
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For further information concerning diseases of crucifers
and other vegetables, contact Mohammad Babadoost, Extension Specialist in Fruit
and Vegetable Diseases, Department of Crop Sciences, University of Illinois at
Urbana-Champaign. University of Illinois
Extension provides equal opportunities in programs and employment.
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